Surface-type illumination devices with a cylindrical light source and a flat polarizer such as the devices described in Japanese Kokai No. 60-205576 and Japanese Kokai No. 61-248079 are well-known. One such example is shown in FIG. 21. In the illumination device 90, cylindrical fluorescent light 92 is positioned on one side of the substantially rectangular and flat polarizer 91. The light introduced to polarizer 91 from fluorescent light 92 is reflected by the diffusion pattern printed on polarizer 91 and emitted from the surface of the polarizer at a fixed density of light.
This type of surface illumination device, in recent years, has been used extensively as backlights for liquid crystal display panels. The use of liquid crystal display panels are increasing as displays in such things as laptop computers, televisions and cameras. The use of liquid crystal display panels for color displays is also increasing. As the size of personal computers and televisions become smaller, it is imperative that liquid crystal display panels become thinner and lighter.
Accordingly, it is necessary that the surface-type illumination device used for liquid crystal display panels as a backlight, in correlation with the color displays, becomes thinner and lighter with less power consumption. Also, to allow for use in color displays, a sufficient brightness is necessary to clearly show the colors displayed in the liquid crystal. This requires the use of a high output fluorescent light in the illumination device. However, along with the light, heat is also radiated from the high-output fluorescent light. The effect of this heat, as shown in FIG. 22, is great. The temperature may rise 30-40.degree. C. above a normal temperature of 25.degree. C. Consequently, when this type of illumination device is used as a backlight in an MIM active color display panel or in a STN passive color display panel, a special method to reduce the heat is necessary to control, to a certain extent, the color and brightness irregularities.
In stead of using one high output fluorescent tube, it is also conceivable to increase the number of fluorescent tubes. In this way, it is possible to control to some extent the temperature increase due to the light source. However, as the number of fluorescent tubes is increased, many other problems appear. One of these problems is the variations in the illumination of the fluorescent tubes. Because the illumination intensity of fluorescent tubes varies according to each tube, it is necessary to adjust such things as the resistance within the fluorescent tube driver circuit to obtain a fixed illumination intensity. Consequently, in the case when several fluorescent tubes are used in one illumination device, extra time is required during the manufacturing process to obtain a balanced and fixed illumination intensity.
Another problem is the increased number of driver circuits required to turn on the fluorescent tubes. The number of these driver circuits can not be easily increased in devices such as microcomputers where thinness and small size are important.
In accordance with the instant invention, a suitable illumination device for color liquid crystal displays can be obtained that are small in size, lightweight, and have high and uniform brightness. Further, it is an object of the invention to provide a surface-type illumination device that can prevent heat generation and its resulting bad effects to the liquid crystal display panel.
Another object of the invention is to provide a surface-type illumination device that, without increasing the number of driver circuits for driving the fluorescent lights, displays a brightness higher than conventional illumination devices and restricts heat radiation.
A further object of the invention is to generate a suitable diffusion pattern to realize a surface-type illumination device, this diffusion pattern being used in the illumination device.
Still another object of the invention is to provide a stable liquid crystal display where the driver IC for driving the liquid crystal display panel is positioned so that it will not be affected by heat.